When Emmitt Smith was drafted by the Dallas Cowboys in 1990, the 20-year-old rookie scored a signing bonus that made him a millionaire overnight. He went on to win three Super Bowls, earn millions more and become the highest-paid running back at the time, after signing a four-year, $13.6 million deal in 1993.

While Smith is the first to admit that he made a few “‘youthful’ financial decisions,” including a $100,000 splurge at age 20, the Hall of Famer also picked up some valuable lessons during his lucrative, 15-season career. And it was Dallas Cowboys owner Jerry Jones who gave him the best money advice he ever received.

“He taught me about finances with a simple statement,” Smith recalls in an interview with CNBC. “He always said, ‘Have a big front door and a small back door. Take in as much as you can, and spend as little as you can.'”

It’s similar to the money advice that basketball legend Shaquille O’Neal lives by. O’Neal, who also spent six figures on a car as a 20-year-old, says if he could give his younger self one piece of money advice, it’s the same thing he would tell any young person today who is coming into a windfall: emphasize saving.

He explained the importance of putting money away with a brilliant analogy while speaking with CNBC’s Bob Pisani at BITG’s Charity Day. “All right, children,” he said, after asking Pisani for a blank sheet of paper. “This is $100,” he continued, motioning to the paper. “What you want to do is, you want to rip the $100 in half.”

Take one half, he said, and “save it. Don’t ever touch it. Put it away. Don’t even look at it. Now you’ve got $50 left. Now, the smart people … the billionaires of the world, they’ll take half of that $50 and put all that away,” he said, adding another quarter of the piece of paper to the “save pile.”

“This right here,” he said of the remaining quarter, is your fun money: “You want to buy houses, you want to buy cars, you want to buy planes, you want to travel? This right here is what you have fun with.”

O’Neal, like Smith, recommends saving and investing the majority of your earnings. Specifically, he says to put 75 percent towards retirement and other long-term goals and live off the remaining 25 percent.

“A guy taught me that a long time ago, and it’s been working for me,” O’Neal told Pisani.